1. Field of the Invention
The present invention relates to an impeller for a fluid transmitting device used for vehicles or industrial machines, including a torque converter and a fluid coupling, and particularly to an improvement in impeller for a fluid transmitting device, including a bowl-shaped or annular shell, a plurality of blades coupled to an inner side of the shell at predetermined locations, an annular retainer plate brazed to an inner side of the shell to retain radially inner ends of the blades, and a hub welded to an inner peripheral edge of the shell.
2. Description of the Related Art
A conventional impeller for a fluid transmitting device is already known, for example, as disclosed in Japanese Patent Publication No. 58-97448.
In the conventional impeller for the fluid transmitting device, in order to weld the shell and the hub to each other, one side of the shell is butted against one side of a positioning flange formed around an outer periphery of the hub, and the attitude of the shell relative to the hub is maintained appropriately and in this state, a fillet welding is carried out between the positioning flange and the shell.
However, if the positioning flange is provided on the hub as described above, the axial wall thickness of the hub is increased by an amount corresponding to the wall thickness of the positioning flange, and also an increase in weight of the hub is provided.
Therefore, it is conceivable that the positioning flange is eliminated, and the inner peripheral edge of the shell is welded directly to an outer peripheral surface of the hub. However, in this case, the axial length of a portion of the shell fitted over the hub is shortened, so that the shell is liable to be inclined with respect to the hub, and it is difficult to maintain an appropriate attitude. Also in this case, there is a possibility that, during welding the shell and the hub to each other, a brazing material which has coupled the shell and retainer plate to each other may be molten by a welding heat to enter a weld zone between the shell and the hub, resulting in a welding defect.
Accordingly, it is an object of the present invention to provide an impeller for a fluid transmitting device, wherein even if the positioning flange is eliminated from the hub, the shell can be supported at an appropriate attitude on the hub and welded to the hub, and the welding defect between the shell and the hub due to melting of the brazing material between the shell and the retainer plate can be prevented.
To achieve the above object, according to a first feature of the present invention, there is provided an impeller for a fluid transmitting device, comprising a bowl-shaped or annular shell, a plurality of blades coupled to an inner side of the shell at predetermined locations, an annular retainer plate brazed to an inner side of the shell to retain radially inner ends of the blades, and a hub welded to an inner peripheral edge of the shell, wherein a cylindrical section is integrally formed at an inner peripheral edge of the shell and bent axially to extend through an inner periphery of the retainer plate, and a brazing material sump for receiving a brazing material molten during brazing of the shell and the retainer plate is provided between an outer peripheral surface of the cylindrical section and an inner peripheral surface of the retainer plate, the cylindrical section being fitted over an outer peripheral surface of the hub and welded to the hub on a side of an outer surface of the shell.
With the first feature, the axial length of a portion where the cylindrical section of the shell is fitted over the hub, can be set sufficiently longer than the wall thickness of the shell, and the shell can be supported on the hub with an appropriate attitude without forming a positioning flange such as that used in the prior art on the hub. Therefore, by welding the cylindrical section to the hub in the above-described state on the side of the outer surface of the shell, the welding accuracy between the shell and the hub can be enhanced. As a result, it is possible to reduce the axial wall thickness of the hub by an amount corresponding to the wall thickness of the positioning flange such as that used in the prior art, leading to a reduction in weight.
Moreover, the cylindrical section can also contribute to an increase in rigidity of a central portion of the shell to increase the coupling strength between the shell and the hub.
In addition, since the brazing material sump is provided between the outer peripheral surface of the cylindrical section and the inner periphery of the retainer plate through which the cylindrical section extends, the outer peripheral surface of the cylindrical section and the inner peripheral edge of the retainer plate are also brazed to each other by the brazing material received in the brazing material sump, and hence the brazing strength of the retainer plate to the shell can be increased.
Moreover, the brazing material received in the brazing material sump is kept retained in the brazing material sump by a capillary phenomenon even if it is molten by a welding heat during welding of the cylindrical section and the hub to each other. Therefore, it is possible to avoid that the molten brazing material enters a weld zone between the cylindrical section and the hub, thereby preventing a welding defect.
According to a second feature of the present invention, in addition to the first feature, the cylindrical section is formed so that it extends through the inner periphery of the retainer plate and protrudes from the inner side of the retainer plate.
With the second feature, even if the brazing material in the brazing material sump is molten by a welding heat during welding of the cylindrical section and the hub, the entrance of the brazing material into the weld zone between the cylindrical section and the hub can be reliably prevented, and at the same time the axial length of fitting of the cylindrical section over the hub can be increased to further stabilize the supporting of the shell on the hub and to further enhance the welding accuracy of the shell and the hub.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.